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DEPARTMENT OF COMMERCE 

BUREAU OF FISHERIES 

HUGH M. SMITH, Commissioner 



THE FLATWORM AS AN ENEMY OF 
FLORIDA OYSTERS 



By ERNEST DANGLADE 

Formerly Field Assistant, U. S. Bureau of Fisheries 



APPENDIX V TO THE REPORT OF THE U. S. COMMISSIONER 

OF Fisheries for 1918 




Bureau of Fisheries Document No. 869 



PRICE, 5 CENTS 

Sold only by the Superintendent of Documents, Government Printing Office, 
Washington, D. C. 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1919 



'^nqgnip*!, 



DEPARTMENT OF COMMERCE 

BUREAU OF FISHERIES 

HUGH M. SMITH, Commissioner 



THE FLATWORM AS AN ENEMY OF 
FLORIDA OYSTERS 



By ERNEST DANGLADE 

Formerly Field Assistant, U. S. Bureati of Fisheries 



Appendix V to the Report of the U. S. Commissioner 
OF Fisheries for 1918 




Bureau of Fisheries Document No. 869 



PRICE, 5 CENTS 

Sold only by the Superintendent of Documents, Government Printing Office, 

Washington, D. C. 



WASHINGTON 

government printing OFFICE 

1919 



d;7 of j^. 

;UL 2 1919 



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5i 



THE FLATWORM AS AN ENEMY OF FLORIDA OYSTERS. 



By Ernest Danglade, Formerly Field Assistant, U. S. Bureau of Fisheries. 



INTRODUCTION. 

During February, 1917, the Bureau of Fisheries and the Florida 
Shell Fish Commission made an investigation of a series of oyster 
areas on both the east and west coasts of Florida with regard to a 
reported destruction of oysters by a parasite, which later proved to 
be a polyclad tm-bellarian, or flatworm. As early as March, 1916, 
Dr. R. E. Coker stated, in unpublished field notes, that a worm, 
known locally as the "leech," was reported to occm* occasionally on 
some of the oyster bars in the vicinity of Tampa, and sometimes to 
cause within a very short time an enormous mortality among the 
planted oysters, and that the fear of the pest served to deter the 
oyster planters from extendmg the cultivated areas. In the latter 
part of^ December of the same year T. R. Hodges, State shell fish 
commissioner of Florida, submitted to the Bureau a number of 
oysters, taken from the beds near Cedar Keys, affected with the so- 
called "leech." The oysters, which had been packed in ice, were 
alive when received in Washington, and contained from 2 to 3 flat- 
worms each; however, the worms were dead, probably having been 
frozen in transit. The attacks of this parasite on oysters in these 
two localities, Tampa and Cedar Keys, are the only ones that had 
ever come to the attention of the Bureau. 

The wi'iter was informed by R. E. Gibson, an oyster dealer and 
planter of Tampa, Fla., that the worms, or so-called "leeches," had 
been observed attackhig the oysters on some of the oyster bars in the 
Tampa Bay region at more or less regular intervals during the past 
20 years, and particularly during the oyster season 10 years ago. 
The worms would disappear entirely from the beds for a period of 2 
or 3 years and then reappear, the reoccurrences apparently running 
in cycles. Compared with the attack of the season 1916-17, the 
previous infestations and mortality were said to have been less 
extensive and harmful. 

On the east coast of Florida a similar outbreak of the worms was 
observed 10 years ago at three or four points on Indian River. The 
principal infected localities in that body of water were Indian River 
Inlet, Bethel Creek, and Orchid. After a very serious and damaging 
attack, from which some oyster bars were practically depleted or 
greatly reduced in productivity, the trouble ceased and has not 
occurred there since. The oyster bars in the meantime have recov- 
ered their normal condition.* It is interesting to note that the de- 
struction of oysters by turbellarians was reported by David G. Stead 

o This information was furnished by E. F. I.lcDonald, a practical fisherman of Port Orange, Fla. 
113671°—! 3 



4 THE FLATWORM AS AN EISTEMY OF FLORIDA OYSTERS. 

from New South Wales in 1907.^ His notes regarding the discovery 
of their mjurious effect upon oysters are of interest: 

A few years ago I found that this worm was known to a few of the oyster farmers of 
Georges River, who had repeatedly observed it amongst oysters on various leases, and 
that they distinguished it under the name of "wafer." As this Aame appears to be 
fairly emtable, I propose for the future to use it in speaking of this worm. Though, 
as I say, the wafer has been known to certain lessees, no delinite connection between 
the oyster and this worm has been shown to exist, and no satisfactory evidence has 
been brought forward to show that the latter was to be added to the already long list 
of oyster pests. However, in the light of recent evidence, I think it will be found 
that this is a pest; that it is at times to be seriously reckoned with, and that it will be 
found to be fairly widespread in our oyster-producing waters. 

At the end of July this year [1907], J. W. Swainson, of Georges River, handed to me 
for determination a number of examples of the wafer, which, he said, was very plen- 
tiful on his leases at that time. No visit was made by me for the pin-pose of investi- 
gating the matter. During the early part of September Fisheries Inspector Latta 
brought in a specimen of an oyster (from a lease in the Hawkesbury River) which was 
in the last stage of destruction by one of these flatworms, and which contained the 
worm itself. This specimen had been handed to Mr. Latta by J. Izzard, who had 
stated that the worm was very plentiful on his leases at Bar Island and Pelican Island , 
and that apparently it was destroying the oysters. Upon this it was so arranged that 
I made a short visit to the locality in question, for the purpose of obtaining more 
definite information. At Bar Island I found the wafer present in large numbers, and 
some were found actually at work between the valves of the o^^sters. Large numbers 
of gaping shells of oysters only recently killed were to be seen on all hands, while the 
same was apparent on Pelican Island (which is submerged at high water). In \dew 
of the very positive evidence obtained at the time, it is only fair to assume that at 
least a part of these — if not all, probably a very large percentage — had succumbed to 
the attacks of the wafer. I must here point out that although the common oyster 
worm (Polydora or Leucodore) was only too abundant on portions of these leases, none 
of the recently dead and gaping shells which I examined showed the least sign of its 
attacks or of the attacks of the common "Drill" or "Borer" (Urosalpinx), although I 
found the latter (previously unrecognized from this locality) to be fairly plentiful. 

It is of interest to mention that at the time of my visit the oysters were all "opening 
very badly " ; that is, they were in poor condition and were likely to remain so until 
the advent of a freshet in the river. 

OCCURRENCE OF THE TURBELLARIAN IN 1916-17. 

The distribution of this turbellarian in sufficient abundance to 
attract attention from oystermen, during the oyster season, 1916-17, 
appears to have been confined to the western coast of Florida, between 
Cedar Keys on the north and Tampa Bay on the south, a distance of 
about 1 10 miles. It was stated that the southern limits had probably 
extended, at some of the earlier periods, as far south as Cape Sable, 
making an approximate range of 300 miles. 

In the vicinity of Cedar Keys, Port Inglis, and Tampa the greater 
number of the oyster bars, especially in the more saline districts, 
were infested and had suffered to a greater or less extent. The con- 
ditions were so bad that, for a time, the industry appeared to be 
seriously threatened. The loss, as reported, ranged from 10 to 20 
per cent of the stock on some beds to the destruction of one entire 
bar. A planted bed of 35 acres in Tampa Bay was attacked by this 
worm and the mature and young oysters alike were said to have 
been completely annihilated. The bed had been planted just two 
years and nad given promise of excellent returns. 

a David G. Stead: Preliminary Note on the Wafer (Leptnplnna australix), a Species of Dcndroconlous 
Turbellarian Worm, Destructive to Oysters. Department of Fisheries, New South Wales, November, 1907; 
pp. 1-6. (No other references to turbellarians attacking oy.sters have come to the writer's attention.) 



THE FLATWORM AS AN" ENEMY OF FLORIDA OYSTERS. 5 

At Port Inglis and Cedar Keys the destruction during the season 
was estimated to be about 30 per cent. One or two locahties, how- 
ever, revealed a mortaUty as great as 90 per cent, but the excess 
should not be attributed to the turbellarian, since many of the empty 
shells or "boxes" contained spat wliich had set before the depreda- 
tions of the worms had occurred, the mortality of these oysters being 
due evidently to other causes. When the devastation was at its 
height the affected oysters, as a rule, contained from 1 to 3 worms, 
although as many as 8 or 10 are said to have been taken from a single 
oyster. During the early part of the season about 100 oysters per 
barrel contained worms, but by February, the time of the examina- 
tion, the trouble had abated to such an extent that not more than 1 
or 2 worms were taken in 20 barrels of stock. It is worthy of remark 
that on the Port Inglis and Cedar Keys bars no small oysters w^ere 
found or reported containing worms, nor did any of the empty shells 
of the small sizes show any malformations indicating that a defensive 
struggle had taken place. 

DESCRIPTION OF THE FLATWORM. 

Although this pest is known to the oyster dealei-s, planters, and 
shuckers of Floricfa as the "leech," it is an animal of very different 
type, belonging to the branch of wormlike animals called platyhel- 
minthes, class turbellaria, and order polycladida.'* Since the general 
character and habits of this turbellarian compare closely with the 
similar pest fomid in New South Wales, and described by Dr. Stead, 
the name "wafer" would be a more suitable and less misleading one 
for common use. 

The worm is almost flat, more or less circular in outline, and 
measures from about one-half to three-quarters inch in diameter. 
It has occasionally been observed, wdien feeding, to be so distended 
that it would cover half the body of the oyster. When disturbed it 
usually rolls up into a sort of a tube, the margins then becoming 
curled and very nregular. The upper surface is drab to dark-brown 
in color, sometimes nearly black, and at times finely stippled with 
darker spots; the central portion, posterior to the eyes, is, as a 
general thing, of a lighter sliade than the remauider of the surface; 
when taken from an alcoholic solution and allowed to dry, a whitish 
mucus coating is observed. The lower surface is whitish to cream 
color. The worm, when removed from the oyster, is soft and slimy, 
and on very moderate pressure breaks up or runs into a jellylike 
mass, apparently without much structure. When placed in alcohol 
of about 75 per cent strength it becomes firm and somewhat leathery. 

PHYSICAL CONDITIONS. 

The turbellarians were found to thrive in only those localities where 
the salinity of the water remained comparatively high, and not in 
areas where decided changes in density caused by freshets occur at 
certain seasons. The temperature is also an important factor in their 
activity and even their existence. If the water is chilled considerably 
below the normal it may cause their complete disappearance or 

a Harry K. Harring, ot the Bureau of Standards and custodian of Kotatoria, U. S. National Museum, is 
engaged in a study of the turbellarian, which will probably prove to be a representative of a new genus. 



6 THE FLATWORM AS AX ENEMY OF FLORIDA OYSTERS. 

perhaps death. During the early part of February, 1917, there was a 
decided fall in the temperature throughout the greater portion of the 
State and many orange trees, early gardens, and much vegetation 
in general were killed; also many small fishes, crabs, and oysters on 
the shallower reefs were destroyed. Following this extrenie, the 
worms practically disappeared from the oyster beds, and relief was 
expressed by those engaged in the oyster industry. Just about this 
time local rains reduced somewhat the salinity of the water, which 
was also an unfavorable condition for the worms. 

Speaking of the turbellarian in New South Wales, Stead says: 
"Judging by my present data, they appear to be most plentiful 
during dry weather (and particularly while mild or high tempera- 
tures prevail), when the water of our estuaries is of greater density." 

Dry, warm weather appears to be the most favorable condition 
for this enemy. The months of their greatest activity on the oyster 
bars are stated to be August and September, and if the weather con- 
tinues warm, October, November, and December may be included. 

The character of the oyster bottoms and the depth of water on 
the bars or reefs do not appear to have any direct influence on the 
depredations committed by the worms, since they were found active 
and damaging at all depths and on all kinds of bottoms, such as sand, 
firm mud, or shells. 

THE ATTACK AND RESULT. 

It is not known how the worm gains admission within the valves 
of the living oyster, and we were not fortunate enough, while exam- 
ining the beds, to obtain any data along this line. It is probable that 
the soft, velvety creature may flatten itself into a very thin wafer- 
like form and slowly work its way between the partially opened 
valves without producing a reaction on the part of the oyster. Some 
oystermen, who have observed the habits of the parasite, are of the 
opinion that the entrance is made along the ventral margin or gilL 
side, about halfway between the hinge and tips rather than at the 
tips themselves, since this is near the point where the worm is usually 
found. The first reaction of the mantle of an infected oyster takes 
place at this mid-portion of the shell. (See fi^s. 1 and 2.) It is 
possible that entrance is made during the larval or immature stage 
of the worm, at a time when admission could be more easily gained, 
and development completed within the oyster. 

Regarding the method of attack the f ollo\ving re'marks are made by 
Stead: 

Method op attack. — After gaining an entrance between the valves of the oyster, 
the wafer proceeds to wrap itself round the upper part of the oyster, as close to the 
great adductor muscle (which so powerfully keeps the two shells shut) as it can get. 
It then proceeds to pour out a great amount of thick, stringy, slimy mucus, which per- 
haps has the effect of partly digesting the body of the oyster, so as to prepare it for 
absorption by the wafer. Certainly in those which have come under my notice, the 
adductor muscle, usually the hardest part of the body of the oyster, is, after being 
attacked by the wafer, ciuite soft, although smelling quite fresh. 

One aspect of the case which is very puzzling is, as to how the worm gains entry 
between the shells of the oyster without the latter "closing down' ' on it; as, if it did, 
the wafer would siu-ely be nipped in two. 

The worm is usually found on the right side of the body of the 
oyster, near the heart, between the adductor muscle and the anterior 



THE FLATWOEM AS AN ENEMY OF FLORIDA OYSTERS. 7 

end or hinge. By carefully opening an infested o5^ster and removing 
the right valve, the worm may be observed as a thin sheet, closely 
adherent to the meat, and more or less covered with a slimy mucus. 
(See fig. 3.) It was stated by the oyster dealer,^ who was interested 
in this subject, that he had found the worms in about the same rela- 
tive position mentioned above, but on the reverse side or between 
the meat and lower valve, so that it was necessary after taking off 
the upper valve to turn the oyster over in order to see the worm. 

It was not determined how long the oyster can successfully with- 
stand an attack or whether it is able to recover after an invasion. 
It is the opinion of some dealers that the oysters are killed within 
two or three days, but this is evidently too brief a period, at least for 
the majority of cases. An exammation of many of the oysters showed 
plainly, both in the meats and shells, that a hard, continuous, and 
defensive sfruggle for existence had taken place. The oysters, which 
were alive when opened, were poor, watery, and shriveled, to a degree 
depending upon the duration of the plague. Being robbed of its 
juices and its vitality probably reduced \)y secretions of the worm, 
starvation and death would ultimately follow. Up to this time no 
odor of decomposition was observed. 

When carefully examined, the meat and shell often reveal the 
successive stages of the battle between the feasting turbellarian 
and the helpless oyster. With a slow but continued loss of its life 
juices and consequently^ contracting meat, the mantle gradually 
withdraws from the margins, particularly along the ventral side, and 
leaves a dark or blackened border or band of shell substance. (See 
fig. 4.) As the struggle continues, a thin ridgelike dej^osit of the 
shell substance may form along the gill side about one-half inch from 
the edge of the shell, and extend from the hinge to the tips. (See 
fig. 5.) At times a second or inner ridge is secreted. (See fig. 6.) The 
oyster, now being reduced to a smaller space by additional loss of its 
juices, has thus accommodated itself to a still smaller shell cavity. 
These ridges are doubtless a mechanical consequence of the shrinkage 
of the oyster; they indicate that the attack is persisted in and that 
considerable time elapses before death ensues. The ridges and other 
deposits are composed of regular shell material — calcium carbonate, 
and conchiolin; nacreous and crystalHne layers are both present. 
(See figs. 7 and 8.) 

CONCLUSIONS AND RECOMMENDATIONS. 

1. Although oysters may be able to resist a brief invasion of the 
turbellarian, it does not appear that they possess the means to ward 
off an assault in harassing numbers, if long continued. 

2. After the turbellarian has once gained admission mthin the 
oyster, there appears to be no method of combating the enemy. The 
defensive ridges deposited by the oyster afford only a temporary 
relief. 

3. It is recommended that a careful working or cultivation of the 
beds in the infested district be carried on systematically, and that 
new, air-dried cultch and fresh seed stock be used when possible. 
All marine grasses and other objects under which the turbellarian 

a Mr. ■Williams, Cedar Keys, Fla. 



8 THE FLATWORM AS AN ENEMY OF FLORIDA OYSTERS. 

may secrete itself or deposit its eggs should be removed from the 
vicinity of the bars. 

4. When it is desired to select a new area for planting and cul- 
tivation, it is advisable, other things being equal, to choose those 
localities where the water has sufficient depth to prevent overheating 
in summer, and also where the salinity may not attain too great a 
degree, as off affluents. 

EXPLANATION OF THE FIGURES. 

[All figures are two-thirds natural size.] 

Fig. 1. Left valve, showing a thiu deposit of shell substance along the ventral margin 
from hinge to tips, and covering nearly one-half of the inner surface of the shell. The 
deposit had curled and peeled somewhat before the photograph was taken. The shell 
is empty. (Taken from Cedar Keys, Fla., Feb. 10, 1917.) 

Fig. 2. Both valves, showing the results of the struggle between the 'oyster and the 
worm. Notice the shell deposits, particularly along the ventral margins. Parts of the 
meat are still clinging to the shell at the muscle scar. The worm had escaped. 
(Taken from Cedar Keys, Fla., Black Point Bars, Feb. 12, 1917.) 

Fig. 3. Left valve with the meat, and the turbellarian in position near the adductor • 
muscle. Notice the shriveled condition of the oyster, and the retreat of the mantle 
fi'om the edges of the shell. The worm had contracted to about one-half of its spread- 
ing capacity. (Taken from Port Inglis, Fla., Feb. 10, 1917.) 

Fig. 4. Left valve with oyster showing the gills. Notice the ' ' ridges " near the hinge 
and along the ventral margin. The ovster was shriveled and dead. The worm had 
escaped. (Taken from Port Inglis, Fla., Feb. 10, 1917.) 

Fig. 5. Left valve, showing that the space occupied by the oyster was reduced, be- 
fore death, about one-half. Notice the "ridge," beginning at the dorsal margin, then 
crossing adjacent to the hinge to the opposite side and extending to the tips. (Taken 
from Cedar Keys, Fla., Feb. 10, 1917.) 

Fig. 6. Left valve, showing the reduced space occupied l)y the oyster just previous 
to death. Notice the two ' ' ridges " or successive stages of retreat along the ventral 
margin, and the spreading out or fan-like condition at the tips. (Taken from Cedar 
Keys, Fla., Feb. 10, 1917.) 

Fig. 7. Both valves, showing shell deposits of conchiolin and calcium carbonate. 
(Taken from Cedar Keys, Fla., Black Pomt Bars, Feb. 12, 1917.) 

Fig. 8. Both valves, showing deposits of conchiolin and calcium carbonate. (Taken 
from Cedar Keys, Fla., Black Point Bars, Feb. 12, 1917.) 




OYSTERS AND SHELLS. SHOWING THE RESULTS OF ATTACK BY FLATWORMS. 



B. F— Doc. 869. 



PLATE II. 




EMPTY SHELLS OF OYSTERS. SHOWING MALFORMATIONS RESULTING FROM 
ATTACKS BY FLATWORMS UPON THE LIVING OYSTER. 



i 



Gaylord Bros. 
Makers 
I Syracuse, N. Y. 
,j PAr. JAN. 21, 1908 



